Systems and methods for measuring ambient and laser temperature in heat assisted magnetic recording

• US 9,074,941 B1
• Filed: 03/14/2013
• Issued: 07/07/2015
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: JP Morgan Chase Bank, N.A. (JP Morgan Chase & Co)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Krichevsky, Alexander, Johnson, Robert J.
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): WILLIAMS, JAMEL E
• Application Number:
  US13/827,089
• Time in Patent Office: 845 Days
• Field of Search: 731/63
• US Class Current: 1/1
• CPC Class Codes: G01K 2217/00 Temperature measurement using electric or magnetic components already present in the system to be measured
• CPC Class Codes: G01K 7/00 Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat giving results other than momentary value of temperature G01K3/00 ; Power supply therefor, e.g. using thermoelectric elements
• CPC Class Codes: G01K 7/01 using semiconducting elements having PN junctions G01K7/02, G01K7/16, G01K7/30 take precedence
• CPC Class Codes: G11B 2005/0021 Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal
• CPC Class Codes: G11B 5/012 Recording on, or reproducing or erasing from, magnetic disks G11B17/00, G11B19/00 take precedence
• CPC Class Codes: G11B 5/02 Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
• CPC Class Codes: G11B 5/40 Protective measures on heads, e.g. against excessive temperature G11B5/31 takes precedence; protection against wear G11B5/255 ; protective structure of the head: see under structures, e.g. G11B5/3106
• CPC Class Codes: G11B 5/5534 Initialisation, calibration, e.g. cylinder "set-up"

Abstract

Systems and methods for measuring ambient and laser temperature in heat assisted magnetic recording (HAMR) systems are provided. One such system includes a slider having a write head, a laser diode coupled to the slider and configured to direct energy to a magnetic medium, and a preamplifier circuit including a voltage measurement circuit configured to measure a voltage drop across the laser diode, and a current measurement circuit configured to measure a current through the laser diode, where the preamplifier circuit is configured to store calibration information including a plurality of temperatures corresponding with measurements of the voltage drop across the laser diode and measurements of the current through the laser diode, and calculate a temperature based on the measured voltage drop across the laser diode, the measured current through the laser diode, and the calibration information.

Claims

1. A system for measuring temperature in a heat assisted magnetic recording, the system comprising:

a slider comprising a write head;

a laser diode coupled to the slider and configured to direct energy to a magnetic medium; and

a preamplifier circuit comprising;

a voltage measurement circuit configured to measure a voltage drop across the laser diode; and

a current measurement circuit configured to measure a current through the laser diode;

wherein the preamplifier circuit is configured to;

store calibration information comprising a plurality of temperatures corresponding with measurements of the voltage drop across the laser diode and measurements of the current through the laser diode; and

calculate a temperature based on the measured voltage drop across the laser diode, the measured current through the laser diode, and the calibration information.

2. The system of claim 1, wherein the calculated temperature is selected from the group consisting of a temperature of the laser diode and an ambient temperature within an enclosure containing the slider, the laser diode, and the magnetic medium.

3. The system of claim 1, wherein the preamplifier circuit is further configured to determine an adjusted current to be supplied to the laser diode based on the calculated temperature.

4. The system of claim 3, wherein the preamplifier circuit is further configured to write information to the magnetic medium while the adjusted current is supplied to the laser diode.

5. The system of claim 1, wherein the preamplifier circuit is further configured to:

compare the calculated temperature with a threshold temperature; and

prevent, if the calculated temperature is greater than the threshold temperature, a flow of current to the laser diode.

6. The system of claim 1:

wherein the voltage measurement circuit comprises a differential amplifier coupled to an anode of the laser diode and a reference voltage;

wherein the current measurement circuit comprises a current to voltage converter coupled to a cathode of the laser diode; and

wherein the preamplifier circuit comprises an analog to digital converter configured to convert analog measurements from the voltage measurement circuit and the current measurement circuit into digital measurements.

7. The system of claim 6:

wherein the differential amplifier of the voltage measurement circuit comprises a non-inverting amplifier configuration;

wherein the current to voltage converter comprises an operational amplifier in an inverting amplifier configuration; and

wherein the analog to digital converter has a resolution of at least 6 bits.

8. The system of claim 1, wherein the plurality of temperatures of the calibration information are measured using a temperature sensor for a calibration to characterize the laser diode.

9. The system of claim 1:

wherein, when a write signal is applied to the write head of the slider, the preamplifier circuit is configured to;

calculate a current to be supplied to the laser diode based on the calculated temperature; and

provide the calculated current to the laser diode.

10. The system of claim 1, wherein the laser diode is configured to direct light energy to a near field transducer configured to cause heating of a portion of the magnetic medium.

11. A method for measuring temperature in a heat assisted magnetic recording, the method comprising:

storing calibration information comprising a plurality of temperatures corresponding with measurements of a voltage drop across a laser diode and measurements of a current through the laser diode;

providing a preselected current to the laser diode;

measuring a voltage drop across the laser diode;

measuring a current through the laser diode;

calculating a temperature based on the measured voltage drop across the laser diode, the measured current through the laser diode, and the calibration information;

determining an adjusted current to be supplied to the laser diode based on the calculated temperature; and

writing information to a magnetic medium using a write head while the adjusted current is supplied to the laser diode, wherein the laser diode is configured to direct light energy on to the magnetic medium.

12. The method of claim 11, wherein the calculated temperature is selected from the group consisting of a temperature of the laser diode and an ambient temperature within an enclosure containing the write head, the laser diode, and the magnetic medium.

13. The method of claim 11, further comprising:

comparing the calculated temperature with a threshold temperature; and

preventing, if the calculated temperature is greater than the threshold temperature, a flow of current to the laser diode.

14. The method of claim 11:

wherein the measuring the voltage drop across the laser diode comprises using a voltage measurement circuit comprising a differential amplifier coupled to an anode of the laser diode and a reference voltage;

wherein the measuring the current through the laser diode comprises using a current measurement circuit comprising a current to voltage converter coupled to a cathode of the laser diode; and

wherein the calculating the temperature based on the voltage drop across the laser diode, the current through the laser diode, and the calibration information comprises using an analog to digital converter configured to convert analog measurements from the voltage measurement circuit and the current measurement circuit into digital measurements.

15. The method of claim 14:

wherein the differential amplifier of the voltage measurement circuit comprises a non-inverting amplifier configuration;

wherein the current to voltage converter comprises an operational amplifier in an inverting amplifier configuration; and

wherein the analog to digital converter has a resolution of at least 6 bits.

16. The method of claim 11, wherein the storing calibration information comprising the plurality of temperatures corresponding with measurements of the voltage drop across the laser diode and measurements of the current through the laser diode comprises measuring the plurality of temperatures of the calibration information using a temperature sensor to characterize the laser diode.

17. The method of claim 11, further comprising:

calculating, when a write signal is applied to the write head of a slider, a current to be supplied to the laser diode based on the calculated temperature when the write signal is applied to the write head; and

providing, when the write signal is applied to the write head of the slider, the calculated current to the laser diode.

18. The method of claim 11, wherein the laser diode is configured to direct light energy to a near field transducer configured to cause heating of a portion of the magnetic medium.